adfa, p. 1, 2011. © Springer-Verlag Berlin Heidelberg 2011 A Computational Study of How and Why reddit.com was an Effective Platform in the Campaign Against SOPA Richard Mills The Psychometrics Centre Department of Psychology University of Cambridge rm747@cam.ac.uk Adam Fish Department of Sociology Lancaster University a.fish2@lancaster.ac.uk Abstract. Successful peer production projects are noteworthy for their leader- less inclusivity, but what specific platform affordances and user activity enable effective collective action? In this paper, we analyze the posting and voting ac- tivities of reddit’s users and show how these interact with the site’s structure to create an environment where information activists could build a resource base to oppose the 2012 US House of Representatives bill, Stop Online Privacy Act (SOPA). Continuing a longitudinal investigation into changes in the ways that user attention and activity is distributed between the site’s 240,000 ‘subreddits’, we conclude by theorizing whether such collective action will be possible on the reddit of the present. Keywords: reddit, Social News, Public Sphere, SOPA 1 Introduction Reddit is a social news site where users submit content and vote to dictate the prominence with which each item will be displayed. It was viewed by 174 million unique users in September 2014 1 . Reddit is divided into more than 240,000 “subred- dits” or content categories (but 50% of these are inactive and have received less than 5 posts in total). According to surveys conducted with reddit’s users in 2010 and 2011, the site’s users are predominantly male, white, young and living in the United States - a survey conducted in 2010 and completed by 25,000 reddit readers found that 40% were white males aged 18-34 living in the United States [1]. Research on Social News platforms has tended to involve either a quantitative ap- proach to describing the functioning of a particular platform as a whole [2–6] or us- ers’ behaviour [7, 8]- or a more qualitative approach to a particular event or phenom- enon which occurred on a Social News platform [9–11]. Published work tends to either focus on the platform itself (without making reference to the content) or on a particular case study (without making reference to how the platform works). This paper combines quantitative approaches to explore how reddit functions with a more 1 www.reddit.com/about